The present invention is concerned with a mechanism for changing dies used in an apparatus for joining workpieces and is more particularly concerned with a self-piercing rivet setting apparatus.
In order to comply with the demand for weight reduction in transport apparatuses or the like, aluminum alloy components have been increasingly employed. Generally, a welding process is not suitable for aluminum panels of automobiles or the like, and such panels are typically fastened together using self-piercing rivets. Particularly in a body assembling operation for automobiles or the like (more particularly in an assembling operation of an aluminum body), self-piercing rivets are used to fasten two or more sheet members (or a sheet member and another component) together.
One example of a self-piercing rivet setting apparatus is disclosed in Japanese Patent Laid-Open Publication No. H 08-505087. A self-piercing rivet may comprise a large diameter head (hereinafter, “large head”) and a hollow leg extending downward from the head. When the self-piercing rivet is driven into a pair of workpieces, the front end of the leg is expandingly deformed while piercing the workpieces, and the workpieces are finally fastened together by the deformed leg and the large head.
The self-piercing rivet may be driven into workpieces to penetrate through a punch-side workpiece but to stay in a die-side workpiece adjacent to a die without penetrating therethrough. Thus, after the rivet setting operation, no opening is formed in the surface of the die-side workpiece. This provides an advantage of preventing deterioration in sealing performance of a workpiece while maintaining good appearance thereof.
FIG. 1 is a sectional view showing a connected region of a pair of workpieces fastened by a conventional self-piercing rivet. The self-piercing rivet comprises a large head 5 and a hollow leg 6 extending downward from the head. The self-piercing rivet is driven into a pair of workpieces 2, 3 by a punch and a die of a rivet setting apparatus (not shown). During the rivet setting operation, the leg 6 is deformed to allow the front end thereof to be expanded while piercing the workpieces (body panels or the like). As a result, the punch-side workpiece 2 and the die-side workpiece 3 are fastened together by the deformed leg 6 and the large head 5. More specifically, the pair of workpieces 2, 3 are fastened together by way of an undercut 7 formed by the leg 6 of the rivet expanded in the lateral direction of the die-side workpiece 3 (or the radially outward direction of the rivet).
The size or dimensions of the rivet may vary depending on the thickness and/or material of workpieces to be fastened. A die to be used in a rivet setting operation for fastening workpieces may need to be changed depending on the thickness and/or material of the workpieces and/or the dimensions of the rivet. When a different die is used, the rivet setting condition for obtaining an optimal undercut may be changed.
Heretofore, in a rivet setting operation for different workpieces, one rivet setting apparatus has been exchanged with another rivet setting apparatus having a different die mounted thereon, or one rivet setting apparatus has been used by substituting one die with another suitable die.
When different rivet setting apparatuses are used, it is necessary to provide a plurality of rivet setting apparatuses suitable for different rivet setting conditions and to transfer workpieces to the respective locations of these apparatuses. As a result, the use of a plurality of rivet setting apparatuses leads to increased equipment cost, expanded installation space and extended time for rivet setting operations. When die substitution is used, it is necessary to change dies in the apparatus frequently, which increases the time needed for riveting operations.